Fluidization is required in thermal air treatment to separate foodstuffs through a continuous process. The term “thermal air treatment” refers to processes such as freezing by means of cold air or gases, drying or heating via introduction of steam, hot air, water or gas. When upwardly rising air is introduced through a perforated trough or foraminous conveyor belt, fluidization of particulate material on the belt, such as foodstuffs, is initiated. In a fluidized state, particulate foodstuffs receive efficient freezing or heating treatment and maintain their particulate nature.
Complete fluidization of foodstuffs results in the material moving in a fluid manner while being treated. Complete fluidization is not always appropriate when dealing with delicate food products such as raspberries or light food products such as diced onions, and it is therefore, important that the level of fluidization be adjustable to accommodate the material being treated.
The creation of fluidized beds of foodstuffs for freezing or heating is a well known technique in the food processing industry. For example, IQF (individually quick frozen) tunnel freezer designs are common in which particulate foodstuffs to be frozen are transported in a fluidized state on a conveyor through an enclosed structure where cooled air is directed upwardly through the foodstuffs. An important aspect of the fluidization process is to create zones of greater and lesser fluidization which assist in maintaining a cascading flow of the product for optimal access of all particles to the upward gas flow through the product. Fluidization techniques have been developed in the past which rely on perforated fixed trays with mechanical agitation and pulsing mechanisms to vary the fluidization within the product bed. Also, fluidization is often initiated with eccentric rollers below a conveyor belt to lift the product and induce product fluidization.
Examples of prior patents employing different techniques for improved transportation and fluidization of foodstuffs include U.S. Pat. No. 6,477,845 to Larsson which relies on a perforated trough with cyclical movement of the trough with and against the direction of product travel to initiate fluidization. U.S. Pat. No. 5,447,040 to Rothstein discloses an endless foraminous conveyor belt with an electric motor having a control unit for periodically driving the belt in a direction opposite to the direction of product travel to initiate fluidization. U.S. Pat. No. 4,301,659 to Martin et al. teaches a conveyor that includes downward steps to cause a thinning of the product bed on the conveyor and increased fluidization by virtue of the velocity of the air being directed through the bed increasing in the region of the thinned product bed.
Prior fluidization techniques tend to rely on manipulation of the conveyor belt by mechanical equipment within the treatment enclosure where cooling or heating is occurring. As such, the equipment is subject to significant wear and tear during normal operation and the cooled or heated treatment enclosure increases the harshness of the operating environment. Therefore, existing mechanical fluidizations systems have a tendency to breakdown during operation resulting in reduction of the effectiveness of fluidization or complete cessation.